When Marshall enters the apartment in the imaginary version of 2006 he is wearing a medal identical to the ones received by Luke Skywalker and Han Solo in Star Wars: Episode IV - A New Hope (1977) and Chewbacca in Star Wars: Episode IX - The Rise of Skywalker (2019); Star Wars being a big part of this episode.
In the imaginary 2003 Ted imagines there is a sandwich on the coffee table. A reference to marijuana that had been used throughout the series.
In the 2006 flash forward, Robin/Rhiannon comes out and speaks French, saying she's French. However, she uses the wrong form of "French." She says, "français," which is only proper if she were a man. She should have said the feminine form, "française," which has a different pronunciation.
The episode, which takes place in 2012, depicts the gang pondering what will happen every three years when they watch the original Star Wars trilogy, with the last future clip depicting them screening the films in 2012. In October of 2012, after the events take place, Disney acquired Lucasfilm and announced that a new Star Wars trilogy was in the works, with Episode VII being ready for release in 2015, which was eventually realized with Star Wars: The Force Awakens.